CN105141555A - System and method for performing channel estimation on an ofdm signal - Google Patents
System and method for performing channel estimation on an ofdm signal Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/0202—Channel estimation
- H04L25/0238—Channel estimation using blind estimation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/0202—Channel estimation
- H04L25/0204—Channel estimation of multiple channels
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/0202—Channel estimation
- H04L25/0212—Channel estimation of impulse response
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
- H04L27/22—Demodulator circuits; Receiver circuits
- H04L27/227—Demodulator circuits; Receiver circuits using coherent demodulation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
Abstract
Embodiments of systems and methods for performing channel estimation on Orthogonal frequency-division multiplexing (OFDM) signals are described. In one embodiment, a method for performing channel estimation on an OFDM signal involves performing blind channel phase estimation on an OFDM signal to obtain channel phase information and performing blind channel magnitude estimation on the OFDM signal to obtain channel magnitude information. Each of performing blind channel phase estimation on the OFDM signal and performing blind channel magnitude estimation on the OFDM signal involves detecting and suppressing a signal path of the OFDM signal. Other embodiments are also described.
Description
Background technology
Channel estimating plays an important role in a communications system.Usually, transmitter inserts the pilot tone of specified quantitative to carrier wave, and corresponding receiver realizes channel estimating.But some communication systems do not have pilot tone or are not enough to carry out the pilot tone of accurate channel estimation.The example of this communication system comprises digital audio broadcasting (DAB) system for digital broadcasting and terrestrial transmission DMB (T-DMB) system.Another example of this communication system is the Vehicular communication system meeting Institute of Electrical and Electric Engineers (IEEE) 802.11p standard, and this Vehicular communication system only has 4 pilot tones in 64 subcarriers usually.For the Vehicular communication system meeting IEEE802.11p standard, due to equipment mobility and long delay path, therefore accurate channel is estimated may be difficult.Not there is pilot tone or be not enough to carry out accurate channel estimation pilot tone and be differential modulation system this communication system (such as, DAB, T-DMB) in, perform demodulation when there is no channel estimating or channel equalization, and use noncoherent receiver to carry out demodulation to modulation signal.Such as, differential demodulator can carry out demodulation when not having channel estimating or channel equalization to differential modulation symbol.Not having the pilot tone that is enough to carry out accurate channel estimation and be in this communication system (such as IEEE802.11P) of coherent modulation system, utilize inaccurate channel estimating and channel equalization to perform demodulation by coherent receiver.
Exist and several shortcomings not utilizing the differential ference spiral of channel estimating or channel equalization to be associated.Such as, first shortcoming is two noise source differential ference spiral processes, and reason is, differential modulation data are character-coded with two.Another shortcoming is, there is following hypothesis: channel almost remains unchanged during two symbols.But this hypothesis is not always set up.Applying in the system of differential modulation in the time domain, channel changes due to equipment mobility.In frequency domain in the system of the continuous subcarrier application differential modulation of OFDM symbol, channel changes due to the frequency selectivity of multipath channel.Especially in single frequency network (SFN) is disposed, frequency selectivity may aggravate, and wherein single frequency network (SFN) disposes that to be usually broadcasted device due to its spectrum efficiency preferred.
In recent years, there are some diverse ways to improve the performance of differential modulation system, and reduced the performance gap between relevant and incoherent reception.A kind of method is that Divsalar and Simon describes (D.Divsalar and M.Simon, " Multiple-symboldifferentialdetectionofMPSK ", IEEETransactionsonCommunications, vol.38, no.3,300-308 page, March nineteen ninety), where it is proposed and use multiple symbol differential detection (MSDD).The method is based on block process, and suppose that channel is at differential modulation symbol block (namely, N in block (wherein N be greater than 1 integer) individual symbol) period is constant, and considers all symbol sebolic addressing possibilities, the symbol sebolic addressing sent to find most probable.Although the method is proved to be effective, the method calculation of complex, that is, the block for N number of D-MPSK modulation signal must compare symbol sequence probability.Mackenthun proposes some shortcut calculations (K.M.Mackenthun for MSDD, Jr " AFastAlgorithmforMultiple-SymbolDifferentialDetectionofM PSK ", IEEETransactionsonCommunications, vol.42, pp.1471 " U1474, in February, 1994/March/April).But the method only considers uncoded system.Certain methods based on grid (trellis) demodulation is described by following people: (the M.Peleg such as Peleg, S.Shamai and S.Galan, " IterativedecodingforcodednoncoherentMPSKcommunicationsov erphase-noisyAWGNchannel ", IEEProceedingsonCommunications, vol.147, no.2, pp.87 " U95, in April, 2000), old (R.-R.Chen such as grade, R.Koetter, U.Madhow and D.Agrawal, " Jointnoncoherentdemodulationanddecodingfortheblockfading channel:apracticalframeworkforapproachingShannoncapacity, IEEETransactionsonCommunications, vol.51, no.10, in October, 2003), with (W.J.vanHoutum such as vanHoutum, F.M.J.Willems, " Jointanditerativedetectionanddecodingofdifferentiallyenc odedCOFDMsystems ", 2010IEEE17thInternationalConferenceonTelecommunications (ICT), vol., no., 36-43 page, 4-7 day in April, 2010).The general character of these methods is: they use grid demodulator, and wherein each state representation of grid is based on the state of the channel phase supposed with the Received signal strength of transmission symbol.The people such as Bahl (L.Bahl, J.Cocke, F.Jelinek, and J.Raviv, " Optimaldecodingoflinearcodesforminimizingsymbolerrorrate (corresp.) " IEEETransactionsonInformationTheory, vol.20, no.2, pp.284 " U287, in March, 1974) people (J.Hagenauer such as grid decoder or Hagenauer that describes, P.Hoeher, " AViterbialgorithmwithsoft-decisionoutputsanditsapplicati ons ", inproc.IEEEGLOBECOM, pp.47.11-47.17, Dallas, Texas, in November, 1989) soft output Viterbi algorithm that proposes is for carrying out generating soft bits according to the network configuration of the remainder that will be fed to receiver chain.These methods are proved to be able to effectively reduce the performance gap between relevant and incoherent reception.But these methods based on grid are also calculation of complex.Such as, these methods based on grid need to have a large amount of trellis state based on grid soft-output demodulator.In addition, when channel changes during the block supposed, these network methods can not correct any phase change usually, and reason is, there is not transition between channel phase state.
Summary of the invention
Describe the embodiment of the system and method for performing channel estimating to OFDM (OFDM) signal.In one embodiment, comprise for method ofdm signal being performed to channel estimating: blind Channel phase estimation is performed to ofdm signal, to obtain channel phase information, and blind Channel amplitude Estimation is performed, to obtain channel magnitude information to ofdm signal.Ofdm signal is performed to blind Channel phase estimation and performs blind Channel amplitude Estimation to ofdm signal and includes: the signal path detecting and suppress ofdm signal.Also describe other embodiments.By detecting and suppressing the signal path of ofdm signal (real pure noise signal path), the quality of reception of different channels (comprising (single frequency network) SFN channel) can be improved, and the coherent demodulation to ofdm signal can be realized.Also describe other embodiments.
In another embodiment, system for performing channel estimating to ofdm signal comprises: channel phase estimation module, be configured to perform blind Channel phase estimation to ofdm signal, to obtain channel phase information, and channel magnitude estimation module, be configured to perform blind Channel amplitude Estimation, to obtain channel magnitude information to ofdm signal.Channel phase estimation module and channel magnitude estimation module are also configured to the signal path detecting and suppress ofdm signal.
In another embodiment, comprise for method ofdm signal being performed to channel estimating: blind Channel phase estimation is performed to ofdm signal, to obtain channel phase information, and blind Channel amplitude Estimation is performed, to obtain channel magnitude information to ofdm signal.Perform channel phase to estimate to relate to: perform exponentiation to ofdm signal, to generate exponentiation signal, inverse fast Fourier transform is performed to exponentiation signal, to generate time-domain signal, detects and remove the pure noise signal path of time-domain signal, to generate treated time-domain signal, fast Fourier transform is performed to treated time-domain signal, to generate frequency-region signal, calculates the phase place of frequency-region signal, and the phase place of frequency-region signal is divided, to obtain channel phase information.Perform channel magnitude to ofdm signal to estimate to relate to: the pure noise signal path detecting and suppress ofdm signal.
According to the following detailed description provided by reference to the accompanying drawings, other aspects of embodiments of the invention and advantage will become apparent, and wherein accompanying drawing is described for principle of the present invention.
Accompanying drawing explanation
Fig. 1 is the schematic block diagram of the OFDM receiver according to inventive embodiment.
Fig. 2 shows the embodiment of the channel estimating unit shown in Fig. 1.
Fig. 3 shows the embodiment of the channel phase estimation module shown in Fig. 2.
Fig. 4 shows the example of the normalization amplitude of ofdm signal.
Fig. 5 shows the example of the normalization amplitude of the ofdm signal shown in Fig. 4 after having tap removing of making an uproar.
Fig. 6 shows the embodiment of the channel magnitude estimation module shown in Fig. 2.
Fig. 7 shows for differential ference spiral and utilizes the signal to noise ratio (SNR) of the coherent demodulation having tap of making an uproar to remove to the chart of the error rate (BER).
Fig. 8 shows the mixing difference/coherent demodulation receiver according to inventive embodiment.
Fig. 9 is for performing the process chart of the method for channel estimating to ofdm signal according to inventive embodiment.
Run through specification, similar Reference numeral can be used to indicate similar element.
Embodiment
Will readily appreciate that, in various different configuration, can arrange and design herein description substantially and the assembly of embodiment illustrated in the accompanying drawings.Therefore, the following detailed description of the various embodiments represented in accompanying drawing is not intended to limit the scope of the present disclosure, but only represents various embodiment.Although present each side of embodiment in the accompanying drawings, unless specifically indicated otherwise, otherwise accompanying drawing need not be drawn in proportion.
Described embodiment is considered to be only illustrative and nonrestrictive in all respects.Therefore, scope of the present invention indicates by appended claim instead of by this detailed description.In the meaning and equivalency range of claim change covered in them scope in.
Run through this specification to feature, advantage or similar language mention do not represent can with the present invention realize all feature and advantage should or in any one embodiment.On the contrary, the language relating to feature and advantage is understood to mean: the special characteristic in conjunction with the embodiments described, advantage or characteristic comprise at least one embodiment.Therefore, run through this specification and need not refer to same embodiment to the discussion of feature and advantage and similar language.
In addition, can in any suitable manner by described feature of the present invention, advantage and property combination in one or more embodiment.Those skilled in the relevant art will recognize according to description herein, can implement the present invention when one or more in the special characteristic not having specific embodiment or advantage.In other instances, the supplementary features that may not present in all embodiments of invention and advantage can be recognized in certain embodiments.
Run through this specification to " embodiment ", " embodiment " mention or similar language means special characteristic that the embodiment combining instruction describes, structure or characteristic comprise at least one embodiment.Therefore, run through the phrase " in one embodiment " of specification, " in an embodiment " and similar language and still must can all not refer to same embodiment.
Fig. 1 is for carrying out the schematic block diagram of the OFDM receiver 100 of demodulation to ofdm signal according to inventive embodiment.In certain embodiments, OFDM receiver is coherent demodulation receiver.In certain embodiments, ofdm signal is differential modulating signal.OFDM (OFDM) uses multiple intensive orthogonal sub-carriers to carry the data on wireless channel.The robustness spread the multipath of channel due to it and its spectral efficient, therefore extensively adopt OFDM in various wireless standard.
In the embodiment shown in fig. 1, OFDM receiver 100 comprises antenna element 102, filter and analog to digital converter (ADC) unit 104, time and Frequency Synchronization unit 106, Cyclic Prefix (CP) and removes and fast Fourier transform (FFT) unit 108, channel estimating unit 110 and coherent demodulator 112.The software (such as, computer instruction) can using hardware (such as processor or receiver circuit) and/or store in computer-readable recording medium (such as, memory, buffer memory, disk) realizes OFDM receiver.Although OFDM receiver is shown as including some assembly in FIG, in certain embodiments, OFDM receiver comprises less or more assembly to realize less or more function.
The antenna element 102 of OFDM receiver 100 is configured to receive ofdm signal.Ofdm signal can be differential modulating signal or non-differential modulation signal.Although antenna element is shown as including an antenna in FIG, in certain embodiments, antenna element comprises less or more assembly and realizes less or more function.
The filter of OFDM receiver 100 and ADC unit 104 are configured to carry out filtering to received ofdm signal, and enter received ofdm signal is converted to digital signal from analog form.
The digital signal that the time of OFDM receiver 100 and Frequency Synchronization unit 106 are configured to receiving from filter and ADC unit 104 performs Domain Synchronous and frequency domain synchronization, to generate synchronous digital signal.
The Cyclic Prefix of OFDM receiver 100 removes and to be configured to FFT unit 108 remove Cyclic Prefix from (receiving from time and Frequency Synchronization unit 106) synchronous digital signal, and fast Fourier transform is performed, with generating process signal to synchronous digital signal.
The channel estimating unit 110 of OFDM receiver 100 is configured to perform channel estimating to the ofdm signal received.In the embodiment shown in fig. 1, channel estimating unit is configured to perform channel estimating to the processing signals removed from Cyclic Prefix and FFT unit 108 receives.Channel estimating unit can produce the channel phase information of estimation and/or the channel magnitude information of estimation.In certain embodiments, channel estimating unit detects and suppresses the signal path of ofdm signal.In wireless channel, the path (being also called tap) of limited quantity carries most of energy.Remaining path is the path/tap of pure noise signal.In certain embodiments, all taps are all made an uproar.But the tap (being also called pure tap of making an uproar) only carrying or comprise noise needs suppressed.Pure noise signal path/tap may be caused by following reason: such as, from the interference of other signal sources, equipment mobility and/or channel circumstance.In certain embodiments, pure noise signal path/tap is the signaling channel with larger signal to noise ratio (SNR).By detecting and suppress the pure noise signal path of ofdm signal, channel estimating unit can provide channel estimating accurately for needing the ofdm system of blind Channel Estimation.Channel estimating unit achieves coherent demodulation and improves the quality of reception of different channels (comprising (single frequency network) SFN channel).
Coherent demodulator 112 is configured to perform coherent demodulation to ofdm signal based on the channel-estimation information from channel estimating unit 110.
Fig. 2 shows the embodiment of the channel estimating unit 110 shown in Fig. 1.In embodiment in fig. 2, channel estimating unit 210 comprises channel phase estimation module 216 and channel magnitude estimation module 218.Channel estimating unit 210 shown in Fig. 2 is the possible embodiments of of the channel estimating unit 110 shown in Fig. 1.But the channel estimating unit 110 shown in Fig. 1 is not limited to the embodiment shown in Fig. 2.
Channel phase estimation module 216 is configured to perform blind Channel phase estimation to ofdm signal, to obtain the shifted version (shiftedversion) of channel phase information or acquisition channel phase information.In some embodiments, blind Channel phase estimation is estimating without any the channel phase performed when reference symbol (such as, frequency pilot sign).Channel phase estimation module can detect and suppress the pure noise signal path of ofdm signal.
Fig. 3 shows the embodiment of the channel phase estimation module 216 shown in Fig. 2.In the embodiment shown in fig. 3, channel phase estimation module 316 comprises exponentiation module 330, inverse fast Fourier transform (IFFT) module 332, tap of making an uproar removing module 334, FFT module 336 and phase place division module 338.The software (such as, computer instruction) can using hardware (such as processor) and/or store in computer-readable recording medium (such as memory, buffer memory, disk) realizes channel phase estimation module.Channel phase estimation module 316 shown in Fig. 3 is the possible embodiments of of the channel phase estimation module 216 shown in Fig. 2.But the channel phase estimation module 216 shown in Fig. 2 is not limited to the embodiment shown in Fig. 3.Such as, although use IFFT module and FFT module in the channel phase estimation module in figure 3, but in other embodiments, the conversion (such as, inverse discrete Fourier transform (IDFT) or discrete Fourier transform (DFT)) of other types can be performed.
Exponentiation module 330 is configured to perform exponentiation, to generate the zoom version (scaledversion) of exponentiation signal or exponentiation signal to ofdm signal.Ofdm signal can be differential modulating signal or non-differential modulation signal.In certain embodiments, exponentiation module be configured to calculate the ofdm signal received M power (M is the integer of power as 2, such as 2,4,8,16 ...) or the zoom version of M power of ofdm signal that receives.Next, as described below, the zoom version of the M power of ofdm signal or the M power of ofdm signal can be used to generate virtual pilot frequency.
In this example, s, H and y are respectively used to represent phase shift keying (PSK) modulation signal, channel and the Received signal strength that send.Send signal s can be expressed as:
Wherein A represents the amplitude sending signal,
M represents the rank that PSK modulates,
D represents the information data that will send.
Channel H can be represented as:
Wherein | H| represents channel magnitude,
represent channel phase.
Received signal strength y can be expressed as:
Wherein | H| represents the amplitude of channel,
represent the phase place of channel,
N represents noise.
In one embodiment, M equals 4 (such as, for quarternary phase-shift keying (QPSK) (QPSK)).The bipyramid of Received signal strength y can be expressed as:
y
4＝H
4s
4+4H
3s
3n+6H
2s
2n
2+4Hsn
3+n
4(4)
If
, and without loss of generality, A is set to equal 1, then and the bipyramid of Received signal strength y can be expressed as:
As disclosed in equation (5), from the signal received, removing the impact of data bit, and obtain the phase place and noise section with 4 times of channels
virtual pilot frequency
use the virtual pilot frequency obtained to estimate channel phase
or
wherein can obtain
and k=1,2,3.Because on the difference between data bit modulation to the OFDM symbol in differential modulation system, as long as therefore apply identical phase shift to two OFDM symbol, the error of 2 π k/4 on channel phase would not cause demodulating error.
Although can derive virtual pilot frequency according to the M power of ofdm signal, these virtual pilot frequencies comprise strong noise usually.In order to reduce the noise in virtual pilot frequency, filtering can be performed between subcarriers or in the time domain between OFDM symbol in a frequency domain.But frequency domain filtering is only applicable to short delayedchannel.When channel be rigid frequency optionally time, the difference between adjacent sub-carrier channel is too large and can not obtain channel estimating accurately.Time-domain filtering is applicable to quiescent conditions, but when relevant device moves everywhere, poor-performing.In embodiment in figure 3, channel phase estimation module 316 uses has tap of making an uproar to remove module 334 to reduce the noise in virtual pilot frequency.
IFFT module 332 is configured to perform inverse fast Fourier transform to obtain/to generate corresponding time-domain signal to the exponentiation signal from exponentiation module 330.Although employ IFFT module in the channel phase estimation module 316 in figure 3, but in other embodiments, the conversion (such as, inverse discrete Fourier transform (IDFT)) of other types can be performed to obtain/to generate corresponding time-domain signal to the exponentiation signal from exponentiation module.
Tap removing module 334 of making an uproar is had to be configured to detect and suppress the pure noise signal path of ofdm signal.Multiple technologies can be used to detect tap be strong path or make an uproar/weak path.In the embodiment shown in fig. 3, there is tap of making an uproar to remove module detection and suppress or remove the pure noise signal path of the time-domain signal from IFFT module 332, to generate treated time-domain signal.In certain embodiments, have tap of making an uproar to remove module the time-domain value of the time-domain signal corresponding with the signal path of time-domain signal and threshold value are compared.In these embodiments, if time-domain value is lower than threshold value, then tap of making an uproar is removed module and time-domain value is reduced to such as 0.In certain embodiments, there is tap of making an uproar to remove module and carry out calculated threshold based on the average of the amplitude of ofdm signal and/or standard deviation, then remove any tap/channel path of amplitude lower than threshold value.In one embodiment, tap of making an uproar is removed module and is used signal to noise ratio (SNR) to carry out definite threshold.In certain embodiments, there is tap of making an uproar to remove the delay statistics that module obtains channel, and use the delay statistics of channel to identify which tap is noise tap.In one embodiment, there is tap of making an uproar to remove the maximum delay of module installation channel, and all taps higher than maximum delay are identified as noise tap.
Fig. 4 is the chart of signal amplitude to the time, it illustrates the example of the normalization amplitude of ofdm signal.Normalization amplitude shown in Fig. 4 is equal to the channel of convolution M time.Fig. 5 is the chart of signal amplitude to the time, it illustrates have tap of making an uproar to remove module 334 performs have tap of making an uproar remove after the example of normalization amplitude of the ofdm signal shown in Fig. 4.As shown in Figure 5, normalization amplitude is noise decrease compared with the normalization amplitude shown in Fig. 4.Module is removed in tap of making an uproar can produce comparatively low noise virtual pilot frequency, and this causes phase estimation more accurately.
Get back to Fig. 3, FFT module 336 is configured to perform fast Fourier transform virtual pilot frequency signal is converted back frequency domain by generating frequency-region signal.In one embodiment, carrying out channel equalization in a frequency domain may be that cost is effective.Although use FFT module in the channel phase estimation module 316 in figure 3, but in other embodiments, the conversion (such as, discrete Fourier transform (DFT)) of other types can be performed virtual pilot frequency signal is converted back frequency domain by generating frequency-region signal.
Phase place divides module 338 and is configured to calculate the phase place from the frequency-region signal of FFT module, and divides the phase place of frequency-region signal, to obtain the shifted version of channel phase information or channel phase information.In an embodiment, phase place divides module and is configured to the phase place calculating each virtual pilot frequency, then divides the phase place calculated, to obtain the shifted version of channel phase information or channel phase information.
Describe the example of the operation of the channel phase estimation module 316 shown in Fig. 3 as follows.Exponentiation module 330 calculate phase shift keying (PSK) modulation signal M power (M is the integer of power as 2, such as 2,4,8,16 ...).M power signal can be represented as:
U＝Y
M(6)
Wherein Y represents phase shift keying (PSK) modulation signal, and U represents the M power of the frequency-region signal of reception, and " Y " and M represent the rank that PSK modulates.IFFT module 332 performs inverse fast Fourier transform to the M power signal of the frequency-region signal received, and to obtain corresponding time-domain signal, it can be represented as:
Z＝IFFT(Y
M)(7)
Wherein Z represents corresponding time-domain signal.Tap of making an uproar is had to remove any noise signal path that module 334 detected based on threshold value and remove time-domain signal.If the time-domain value Z (i) of time-domain signal (i is integer) is corresponding with the signaling channel/tap lower than threshold value, then time-domain value Z (i) is set to 0.Otherwise time-domain value Z (i) remains unchanged.Before tap of making an uproar is removed, discrete time signal Z (1: 10) can be represented as [Z (1), Z (2), Z (3), Z (4), Z (5), Z (6), Z (7), Z (8), Z (9), Z (10)].In ABS (Z (1: 10))=[1,10,11,9,1,2,1,1,2,15] (ABS is the function of the absolute value for calculated complex) and threshold value is set in the example of 3.5 (or numbers of any appropriate), Z (1), Z (5), Z (6), Z (7), Z (8) and Z (9) substitute by 0, and reason is that the respective absolute values of these time domain numbers is less than threshold value 3.5.After tap of making an uproar is removed, Z (1: 10) becomes [0, Z (2), Z (3), Z (4), 0,0,0,0,0, Z (10)].FFT module 336 performs fast Fourier transform so that virtual pilot frequency signal is converted back frequency-region signal, and it can be expressed as:
Z′＝FFT(z′)(8)
Wherein Z ' represents frequency-region signal and z ' represents by there being tap of making an uproar to remove the signal of CMOS macro cell.Phase place divides the phase place that module 338 calculates frequency-region signal, and by the phase place of frequency-region signal divided by M, to obtain the shifted version of channel phase information or channel phase information.The shifted version of channel phase or channel phase can be represented as:
Wherein C_phase represents the shifted version (such as have the channel phase of 2*pi*k/M, k is positive integer) of channel phase or channel phase, and Z ' represents corresponding frequency-region signal, and M represents the rank that PSK modulates.
For non-differential modulating system (such as IEEE802.11p), also can apply by channel phase estimation module 316 tap of making an uproar and remove.When modulation is not MPSK, other technologies can be used to generate virtual pilot frequency.Such as, the output (such as Viterbi, turbo, LDPC etc.) of channel decoder may be used for generating virtual pilot tone.
Return Fig. 2, channel magnitude estimation module 218 is configured to: perform blind Channel amplitude Estimation, to obtain channel magnitude information to the ofdm signal received.In certain embodiments, blind Channel amplitude Estimation is estimating without any the channel magnitude performed when reference symbol (such as, frequency pilot sign).Channel magnitude estimation module can detect and suppress the noise signal path of ofdm signal.
Fig. 6 shows the embodiment of the channel phase estimation module 218 shown in Fig. 2.In embodiment in figure 6, channel magnitude estimation module 618 comprises: magnitude computation module 630, inverse fast Fourier transform (IFFT) module 632, tap of making an uproar remove module 634 and FFT module 636.Because data bit does not affect channel magnitude, therefore can use original received signal instead of ask the signal after M power.Therefore, the output of FFT module is the final result that channel magnitude is estimated.Channel magnitude estimation module can be realized with hardware (such as processor) and/or the software (such as computer instruction) stored in computer-readable recording medium (such as memory, buffer memory, disk).Channel magnitude estimation module 618 shown in Fig. 6 is that of the channel magnitude estimation module 218 shown in Fig. 2 may embodiment.But the channel magnitude estimation module 218 shown in Fig. 2 is not limited to the embodiment shown in Fig. 6.Such as, although employ IFFT module and FFT module in the channel magnitude estimation module in figure 6, but in other embodiments, the conversion (such as, inverse discrete Fourier transform (IDFT) or discrete Fourier transform (DFT)) of other types can be performed.
Magnitude computation module 630 is configured to the amplitude calculating ofdm signal.IFFT module 632 is configured to perform inverse fast Fourier transform, to generate time-domain signal to ofdm signal.In certain embodiments, the conversion (such as, inverse discrete Fourier transform (IDFT)) of other types can be performed to generate time-domain signal to ofdm signal.Tap removing module 634 of making an uproar is had to be configured to detect and suppress the pure noise signal path of time-domain signal, to generate treated time-domain signal.FFT module 636 is configured to perform fast Fourier transform, to obtain channel magnitude information to treated time-domain signal.In certain embodiments, the conversion (such as, discrete Fourier transform (DFT)) of other types can be performed to treated time-domain signal, to obtain channel magnitude information.
The following describe the example of the operation of the channel magnitude estimation module 618 shown in Fig. 6.Magnitude computation module 630 calculates the amplitude of ofdm signal.Amplitude can be expressed as:
A＝|Y|(10)
Wherein Y represents the ofdm signal of reception, and A represents amplitude.IFFT module 632 performs inverse fast Fourier transform to the ofdm signal received, and to obtain corresponding time-domain signal, it can be expressed as:
a＝IFFT(A)(11)
Wherein a represents corresponding time-domain signal.Tap of making an uproar is had to remove the pure noise signal path that module 634 detected based on threshold value and remove time-domain signal.If lower than threshold value, then time domain letter value Z (i) is set to zero to the time-domain value Z (i) of time-domain signal (i is integer).Otherwise time-domain value Z (i) remains unchanged.FFT module 636 performs fast Fourier transform and is converted to frequency-region signal with the treated signal that module 634 is removed in own tap of making an uproar in the future, and it can be expressed as:
A′＝FFT(a′)(12)
Wherein A ' represents corresponding frequency-region signal and a ' indicates that the signal of CMOS macro cell is removed in tap of making an uproar.
Fig. 7 shows by using the example having the improvement in performance of tap clearance technique of making an uproar.Particularly, Fig. 7 is for differential ference spiral and utilizes the signal to noise ratio (SNR) of the coherent demodulation having tap of making an uproar to remove to the chart of the error rate (BER).Result shown in Fig. 7 is based on DAB system, and DAB system uses differential QPSK modulation, and in differential QPSK modulation, maximum Doppler frequency is set to 50Hz.In the figure 7, channel estimating unit 210 introduces the decay of 1.25dB in signal to noise ratio (SNR), to reach 10
-4target error rate.
Tap clearance technique of making an uproar is applicable to majority of case.But, if the too much channel energy of the enough noise of non-filtering or filtering, then, compared with differential ference spiral, there is the performance of tap clearance technique of making an uproar to decline.In order to avoid performance loss, receiver can check whether the relatively accurate channel estimating that can realize for coherent demodulation.If can not realize the relatively accurate channel estimating for coherent demodulation, then receiver can be switched to traditional differential ference spiral.Fig. 8 shows the mixing difference/relevant OFDM receiver 800 according to inventive embodiment.In embodiment in fig. 8, mixing OFDM receiver comprises antenna element 102, filter for receiver and ADC unit 104, time and Frequency Synchronization unit 106, CP and removes and fast Fourier transform (FFT) unit 108, channel estimating unit 110, coherent demodulator 112, two multiplexer 814-1,814-2, detecting unit 820 and differential demodulator 822.Detecting unit is configured to the result detecting channel estimating unit 110, and makes coherent demodulator or differential demodulator carry out demodulation to ofdm signal.In certain embodiments, detecting unit is configured to, based on from the channel phase information of channel estimating unit and channel magnitude information, check the quantity of the survival signaling pathway/tap of ofdm signal.If the quantity of survival tap is less than threshold value, then use coherent demodulator, and coherent demodulation is performed to ofdm signal.If the quantity of survival tap is greater than threshold value, then virtual pilot frequency is confirmed as making an uproar very much and can not providing channel estimating accurately.Next, adopt differential ference spiral, and come to perform differential ference spiral to ofdm signal by controlling multiplexer.
Fig. 9 is for performing the process chart of the method for channel estimating to ofdm signal according to inventive embodiment.At frame 902 place, blind Channel phase estimation is performed, to obtain channel phase information to ofdm signal.At frame 904 place, blind Channel amplitude Estimation is performed, to obtain channel magnitude information to ofdm signal.Ofdm signal is performed to blind Channel phase estimation and performs blind Channel amplitude Estimation to ofdm signal and includes: the signal path detecting and suppress ofdm signal.
Although illustrate and describe the operation of method herein with particular order, the order of the operation of method can change, and makes it possible to perform some operation by contrary order, or make it possible at least partly and other operate and perform some simultaneously and operate.In another embodiment, instruction or the child-operation of different operating can be realized by the mode of being interrupted and/or replace.
In addition, although to have described or the specific embodiment of the present invention that illustrates comprises the some assemblies describing or illustrate herein, other embodiments of the present invention can comprise less or more assembly and realize less or more feature.
In addition, although described and shown the specific embodiment of invention, the invention is not restricted to particular form or the layout of the part describing like this and illustrate.Scope of the present invention is limited by claims and equivalents thereof.
Claims (20)
1., for performing a method for channel estimating to OFDM signal, described method comprises:
Blind Channel phase estimation is performed, to obtain channel phase information to ofdm signal; And
Blind Channel amplitude Estimation is performed, to obtain channel magnitude information to described ofdm signal;
Wherein ofdm signal is performed to blind Channel phase estimation and performs blind Channel amplitude Estimation to described ofdm signal and include: the signal path detecting and suppress described ofdm signal.
2. method according to claim 1, wherein, described ofdm signal is differential modulating signal.
3. method according to claim 1, wherein, performs blind Channel phase estimation to ofdm signal and also comprises: perform exponentiation, to generate exponentiation signal to described ofdm signal.
4. method according to claim 3, wherein, performs blind Channel phase estimation to ofdm signal and also comprises: perform conversion, to generate time-domain signal to described exponentiation signal.
5. method according to claim 4, wherein, performs blind Channel phase estimation to ofdm signal and comprises: the pure noise signal path detecting and suppress described time-domain signal, to generate treated time-domain signal.
6. method according to claim 5, wherein, detects and suppresses the pure noise signal path of described time-domain signal to comprise: the pure noise signal path removing described time-domain signal.
7. method according to claim 5, wherein, detects and suppresses the pure noise signal path of described time-domain signal to comprise: described time-domain signal and threshold value being compared.
8. method according to claim 5, wherein, detects and suppresses the pure noise signal path of described time-domain signal to comprise:
The time-domain value of described time-domain signal and threshold value are compared, wherein, described time-domain value is corresponding with the signal path of described time-domain signal; And
If described time-domain value is lower than described threshold value, then reduce described time-domain value.
9. method according to claim 7, wherein, reduces described time-domain value and comprises: if described time-domain value is lower than described threshold value, then described time-domain value is set to 0.
10. method according to claim 5, wherein, performs blind Channel phase estimation to ofdm signal and also comprises: perform fast Fourier transform, to generate frequency-region signal to described treated time-domain signal.
11. methods according to claim 10, wherein, perform blind Channel phase estimation to ofdm signal and also comprise:
Calculate the phase place of described frequency-region signal; And
The phase place of described frequency-region signal is divided, to obtain described channel phase information.
12. methods according to claim 1, wherein, perform blind Channel amplitude Estimation to described ofdm signal and also comprise:
Calculate the amplitude of described ofdm signal; And
Inverse fast Fourier transform is performed, to generate time-domain signal to the amplitude of described ofdm signal.
13. methods according to claim 12, wherein, perform blind Channel amplitude Estimation to described ofdm signal and comprise:
Detect and suppress the pure noise signal path of described time-domain signal, to generate treated time-domain signal; And
Fast Fourier transform is performed, to obtain described channel magnitude information to described treated time-domain signal.
14. methods according to claim 1, wherein, described ofdm signal is phase shift keying psk modulation signal.
15. methods according to claim 1, also comprise:
The quantity of the survival signaling pathway of described ofdm signal is determined based on described channel phase information and described channel magnitude information;
If the quantity of described survival signaling pathway is less than threshold value, then coherent demodulation is performed to described ofdm signal; And
If the quantity of described survival signaling pathway is greater than threshold value, then differential ference spiral is performed to described ofdm signal.
16. 1 kinds for performing the system of channel estimating to OFDM signal, described system comprises:
Channel phase estimation module, is configured to perform blind Channel phase estimation, to obtain channel phase information to ofdm signal; And
Channel magnitude estimation module, is configured to perform blind Channel amplitude Estimation to described ofdm signal, estimates to obtain channel magnitude,
Wherein said channel phase estimation module and described channel magnitude estimation module are configured to the signal path detecting and suppress described ofdm signal.
17. systems according to claim 16, wherein, described ofdm signal is differential modulating signal.
18. systems according to claim 16, wherein, described channel phase estimation module is configured to:
Exponentiation is performed to generate exponentiation signal to described ofdm signal;
Inverse fast Fourier transform is performed to generate time-domain signal to described exponentiation signal;
Detect and suppress the pure noise signal path of described time-domain signal, to generate treated time-domain signal;
Fast Fourier transform is performed, to generate frequency-region signal to described treated time-domain signal;
Calculate the phase place of described frequency-region signal; And
The phase place of described frequency-region signal is divided, to obtain described channel phase information.
19. systems according to claim 16, wherein, described channel magnitude estimation module is configured to:
Calculate the amplitude of described ofdm signal;
Inverse fast Fourier transform is performed, to generate time-domain signal to the amplitude of described ofdm signal;
Detect and suppress the pure noise signal path of described time-domain signal, to generate treated time-domain signal; And
Fast Fourier transform is performed, to obtain described channel magnitude information to described treated time-domain signal.
20. 1 kinds for performing the method for channel estimating to OFDM signal, described method comprises:
Blind Channel phase estimation is performed to ofdm signal, to obtain channel phase information, wherein performs channel phase and estimate to comprise:
Exponentiation is performed, to generate exponentiation signal to described ofdm signal;
Inverse fast Fourier transform is performed, to generate time-domain signal to described exponentiation signal;
Detect and remove the pure noise signal path of described time-domain signal, to generate treated time-domain signal;
Fast Fourier transform is performed, to generate frequency-region signal to described treated time-domain signal;
Calculate the phase place of described frequency-region signal; And
The phase place of described frequency-region signal is divided, to obtain described channel phase information; And
Blind Channel amplitude Estimation is performed to described ofdm signal, to obtain channel magnitude information, wherein blind Channel amplitude Estimation is performed to described ofdm signal and comprise: the pure noise signal path detecting and suppress described ofdm signal.
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| US14/287,778 US9608844B2 (en) | 2014-05-27 | 2014-05-27 | System and method for performing channel estimation on an OFDM signal |
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| US9608844B2 (en) | 2017-03-28 |
| EP2950491A1 (en) | 2015-12-02 |
| CN105141555B (en) | 2018-08-24 |
| EP2950491B1 (en) | 2019-04-03 |
| US20150349981A1 (en) | 2015-12-03 |
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